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Topic: General ISS Q&A thread (Read 661771 times)

There are 2 excellent Shuttle Q&A threads in the general discussion forum. I've really enjoyed both even if I've not posted. On the ISS forum however the questions are rather diversified over several threads which makes searching difficult and as a result sometimes causes doubling up of questions. I thought it would be a good idea to start a general ISS Q&A thread to serve as a knowledge centre for all readers and posters that have questions about the ISS. (There is an ISS assembly questions thread, but I was thinking more of a general questions thread.)

I'll start of with a few questions of my own:

1. Laundry. You hear a lot about the 'common tasks' that are a little different in space. Examples are food, hygiene, etc. However I have never heard how/if astronauts wash their clothing on the ISS. On the other hand, you do hear a lot about 'new sets of clothes' being brought up and dirty clothes being brought down. Is there no washing machine on the ISS? If not, is it too difficult/expensive to design one?

2. Oxygen generation. I know that the STS-121 mission brought up a new oxygen generator to the ISS that, when working together with the russian Elektron oxygen generator, will provide oxygen capacity for roughly 4 persons. Is this generator already tested/turned on? If not, how to provide oxygen currently for 3 persons? (Elektron provides oxygen for 2) And, when will it be turned on?

3. PVR's. I've never quite understood how these work, can anyone give a brief explanation?

That should be enough for a kick off. Moderators, if this is considered a bad idea or if you don't like it for any other reason, feel free to modify/delete it. Regards,Spiff

No washing machine. If you consider, it's pretty obvious - it's much cheaper to lift clean clothes to orbit than the much larger mass of water needed for washing those clothes (and thus wasted). Also, how would you dry them?

Not sure what you mean, exactly, about how the PVR's work, apart from being solar cell arrays.

I'm not sure either, but he could be referring to the Photo Voltaic Radiators on each of the truss segments.

(Common point of confusion: those radiators don't literally cool the solar arrays... there are no coolant lines running through them. The radiators are there to cool all the batteries and electronics stuffed inside the truss segment.)-- JRF

OK, yeah, that makes some sense. Some folks do wonder why spacecraft (or the ISS) would need radiators.After all, they're in space where it's usually cold, right?

Electronics, especially power conversion and distribution modules, aren't 100% efficient - meaning a percentage of the input power gets converted to heat. Just like your average PC needs its own heat sink, electronics in space need their own heat sinks and a way to radiate that heat into space.

Since there's no air to distribute the heat into (and you don't want it done into the crew modules) you need a way to take the heat from the electronics and transfer it to a large enough space radiator for efficient heat dissipation.

Power converter and distribution electronics generate a lot of heat (lots of power, combined with less than 100% conversion efficiency). Liquid cooling works best in those cases, and running that heated fluid through large radiators exposed to space converts the heat in the fluid to infrared radiant energy, which in turn cools the fluid.

The same thing is done with Shuttle orbiters and their payload bay door radiators. The difference is the ISS uses long panel arrays, instead.

what do astronaust wear in space during their stays at the station and how long is a set of clothes considered to be good for before it is taken back to earth and before astronauts launch do they get to pick what clothes will be launched up to them later in their mission or do they just have to live with what they get?

IIRC, much of the clothing is aready sized and fit for them some months before their flights. A few items are returned (probably the most expensive to make), but I gather a lot of clothing is dumped into a disposal bag for Progress or a future MPLM for disposal.

I don't know what would sort of time or wear period would be considered for classification as 'dirty', but I'd guess that clothing worn during exercise periods would be discarded much more quickly than others (or more specialized clothing, like mission jumpsuits or fluid-control pants).

yea, I mean the radiators, not the solar arrays themselves. And, I gathered more or less that that's how they're supposed to work, but, I don't quite see how that could work during orbital day when the sun is shining rather brightly on those same radiators. Are they only turned on during night? Also, how can you radiate heat into the vacuum of space?

IOW, I kinda get it, but not completely.

Oh yea, and about the washing machine. That kinda makes sense, but still, I guess there could also be developed a system that could filter the water and use it again. And a dryer could also be developed I suppose....Then again, probably it's not that obvious, or they would have done so long ago...

Spiff - 16/9/2006 4:22 PMyea, I mean the radiators, not the solar arrays themselves. And, I gathered more or less that that's how they're supposed to work, but, I don't quite see how that could work during orbital day when the sun is shining rather brightly on those same radiators. Are they only turned on during night? Also, how can you radiate heat into the vacuum of space? .

They face away and on edge to the sun.

Basic physics. Heat transfer is but 3 methods. conductive, convective and radiant. Radiant needs no medium to work. Just a temp difference

No washing machine. If you consider, it's pretty obvious - it's much cheaper to lift clean clothes to orbit than the much larger mass of water needed for washing those clothes (and thus wasted). Also, how would you dry them?

You can do laundry up there, after a fashion: Ken Bowersox demonstrated in one of the Expedition 6 videos (last one at bottom of page) how to wash favorite items of clothing: the clothes are first put into a plastic bag, into which is squirted water and soap. After several minutes of squeezing and prodding, the clothes are taken out and rinsed with more water in a separate bag. Russian wet/dry towels are used to squeeze as much water out as possible, then the clothes are secured behind bungee cords in Zarya to dry, which they do after around three hours. All evaporated water is reclaimed by the SRV-K2M condensate water processor that separates it into gas and liquid, then purifies and recycles the evaporate as potable water.

2. Oxygen generation. I know that the STS-121 mission brought up a new oxygen generator to the ISS that, when working together with the russian Elektron oxygen generator, will provide oxygen capacity for roughly 4 persons. Is this generator already tested/turned on? If not, how to provide oxygen currently for 3 persons? (Elektron provides oxygen for 2) And, when will it be turned on?

NASA has moved up the launch of a new oxygen generator, which will fly to the International Space Station as soon as 2007.

It not only will provide a backup for the frequently troubled Russian oxygen generator, the Elektron, but it will support expansion of the station crew, officials said.

"Having another system up there helps build redundancy into the system and helps make the station more robust," said Dave Parker, manager for the project at Hamilton Sundstrand.

The company is developing the generator and plans to deliver it to NASA's Marshall Space Flight Center next month, so it can be integrated with its power supply.

Kennedy Space Center should get the generator by the end of the year, said Marshall's Bob Bagdigian, manager for the Regenerative Environmental Control Life Support System.

It's scheduled to fly in a cargo module about May 2007, he said, depending on how the schedule unfolds when the shuttles start flying this May.

It will be installed in the station's U.S. laboratory. Previously, it was to be housed in the yet-to-fly European-built Node 3.

If there were an earlier opportunity to fly the new oxygen generator, "the program would like to take advantage of that," Bagdigian said. It could be a backup for the Elektron sooner, and an earlier delivery would allow testing of its systems before the crew is expanded beyond two or three people.

"We'd like to get to orbit as soon as we can and do some checkout on it and make sure everything's in order before the program has to depend on it," he said.

The Elektron and the new system convert water into oxygen and hydrogen through electrolysis. An electrolyte is needed to complete the electrical circuit that makes the process work. The bubble-prone Russian system uses a liquid electrolyte, but the new U.S. system uses a solid one, Bagdigian said.

"You don't have to worry about the electrolyte leaking," he said.

"We've been building this basic technology in a lot of different forms for different customers over the years," including Navy submarines, Hamilton Sundstrand's Parker said. The difference is that the space hardware must be small and light and use as little power as possible.

The company, which produces a lot of space and spacesuit hardware, is working closely with NASA to make sure the generator is safe, Parker said.

"It has to be handled very, very carefully," he said.

"We're looking forward to delivering it," Bagdigian said. "We think it will be a useful addition to the program and one that will give them a lot more on-orbit capability and flexibility."

I'm hoping the new oxygen generator will work well. Don't get me wrong, I think the Elektron is a magnificent machine despite it's temper. But it will be good to have two systems in order to provide redundancy.

Additional question. From Suzy's link: The decomposition of 1 kg (2.2 lbs) of water yields 25 L (0.88 ft3) of oxygen per hour at a pressure of 760 mmHg, which is enough to support one crew member for one day.That would mean that if you run the system 24 hours per day you could theoretically provide oxygen for 24 people. Right? So why have I seen it listed so far as supporting a maximum of 2 persons? Limited water supply?The OGS provides approx. 6 kg of oxygen per day normally. (Six crewmembers) Is this at 24 hour/day operation? Or does it run only a few hours per day (as elektron seems to do.)

How do the different docking mechanisms (APAS, CBM, Russian (don't know the name of the russian system) ) compare in terms of inner diameter? IOW, what is the maximum payload diameter that can be taken up by soyuz/progress/ATV (Russian docking) MPLM/HTV (CBM) and Shuttle (APAS)?